GNA regulates rice spikelet formation via DEP1-enhanced repression of OsCKX2 and cytokinin modulation

Rice yield is directly influenced by spikelet number, a trait governed by both genetic and hormonal regulatory pathways. In this study, we demonstrate that GNA, a GRAS family transcription factor, acts as a key positive regulator of spikelet development in rice. Through map-based cloning, transgenic manipulation, and molecular assays, we show that GNA enhances grain number per panicle by repressing OsCKX2, a cytokinin oxidase gene responsible for cytokinin degradation. Chromatin immunoprecipitation, luciferase activity assays, and electrophoretic mobility shift assays (EMSA) confirm that GNA directly binds to the OsCKX2 promoter, suppressing its transcription and thereby elevating endogenous cytokinin levels. Notably, GNA physically interacts with DEP1/dep1, and this interaction further enhances the GNA-mediated repression of OsCKX2. Overexpression of GNA significantly increases spikelet number, pedicel branching, and grain yield per plant, accompanied by the activation of cytokinin-responsive genes. These findings reveal a previously uncharacterized DEP1-GNA-OsCKX2 regulatory module that links G-protein signaling with cytokinin signaling and panicle morphogenesis, providing a promising genetic target for rice yield improvement and molecular breeding.